In the processing of materials containing metal values, two of the main extractive methods to be considered are pyrometallurgy and hydrometallurgy. In the former, a metal-containing material such as ore, slag, scrap, etc., is heated with appropriate agents such as reducing agents, fluxing agents, sulfidizing agents, chloridizing agents and/or oxidizing agents, etc., usually the melting or fusion point of the mixture. At this temperature, there is generally a separation of metallic values from gangue or waste materials. The procedure then calls for separating the metallic values from slag or waste material at a temperature at which both are molten. The phase containing the metal value is then cast to some convenient shape for use or for further refining, whichever is appropriate for the particular system involved. The very high temperatures involved in this technique are achieved via electric furnaces, blast furnaces, reverberatory furnaces, etc. Temperatures required for metals such as copper, nickel, iron would generally range from 1000.degree. C. to 2000.degree. C. An advantage in this method is that recoveries of the metal values are typically quite high.
The hydrometallurgy approach differs substantially from pyrometallurgy in that, although the metal-bearing material such as ore, slag, scrap, etc., may be heated with agents such as reducing agents, oxidizing agents, sulfidizing and chloridizing agents as part of the procedure, the temperatures involved are generally much lower than with the usual pyrometallurgical method. These temperatures typically may be 260.degree. to about 1040.degree. C., temperatures generally well below the fusion point of the metal-containing material.
Following this step, the treated metal-containing material then is contacted with an appropriate aqueous solution for extracting metal values by dissolution. The metal is then removed from the solution by precipitation, solvent extraction, evaporation of solvent, etc. The metal-containing residue obtained is then handled appropriately to further refine the metal. Although conditions of temperature are generally much lower than in pyrometallurgy, it is frequently found that recovery of the metal values is also lower than in the pyrometallurgical method.
A particular case where this is true concerns the extraction of nickel from lateritic nickel ores. The pyrometallurgical processes range from the use of an electric furnace for the direct smelting of ore to produce ferronickel through similar techniques involving the blast furnace in which an iron-nickel-sulfide matte is obtained. The extraction of nickel from the ore using this method is greater than 90%.
Of the several hydrometallurgy approaches used commercially for treating this type of ore, the practice on a limonite ore or a highly serpentinic ore, such as that at Nicaro, Cuba, involves roasting the ore in a multiple hearth furnace while a reducing gas such as producer gas passes countercurrent to the ore. Temperatures in this case range from about 485.degree. to about 735.degree. C. Following the roasting step, the ore is cooled in the absence of air, mixed with an ammoniacal ammonium carbonate solution and vigorously agitated and aerated. This results in the dissolution of nickel, copper and cobalt, separating them from the bulk of the ore. This solution then is treated with steam, driving off ammonia and precipitating nickel carbonate. This product then is treated further to obtain the appropriate form of nickel or use as such. In comparison to the pyrometallurgical process, however, extractions using this method have only been of the order of 70 to 80 percent.
Several United States Patents have disclosed processes such as that hereinbefore described. Among these patents are U.S. Pat. Nos. 3,845,189, 3,772,423, 3,772,424 and 3,661,564. These patents describe a hydrometallurgical method utilizing additives comprising aqueous solutions of hydrogen chloride, hydrogen bromide, gaseous sulfur compounds such as hydrogen sulfide, sulfur dioxide, etc., as well as elemental sulfur which are utilized to treat the metal-bearing source.
Several other hydrometallurgy methods involve the use of procedures which include a roasting step with chlorides or sulfates, but in other than reducing atmospheres and in such a manner as to form soluble metal salts, and the roasted ore is leached with an appropriate solvent such as dilute sulfuric acid. Alternatively, in certain cases the ore can be leached directly, such as with sulfuric acid solution, but this is practical only when the magnesia content of the ore is low.
It has now become increasingly important to recover all of the various metals which are present in metal-bearing sources such as ores. Although the above set forth patents are concerned primarily with the recovery of nickel, it has become increasingly important that metals such as cobalt be recovered from metal-bearing sources such as lateritic ores due to the fact that the use of cobalt is becoming more important in the chemical industry as well as other industries such as metal fabrication, ceramics, etc. The principal use of cobalt is in alloys, especially cobalt steels where it is used for permanent supermagnets as well as cobalt-chromium high speed tool steels. In addition, cobalt alloys are also used where high temperatures are present such as in jet engines.
British Patent Specification No. 1,355,535 discloses a method for the extraction of metals from solution. In this patent, ammonia or a derivative thereof is added for the purpose of forming a soluble amine or amine-type complex to a solution of metal. The ammonia is added to the metal solution in an amount at least sufficient to satisfy the stoichiometric requirements for the formation and stabilization of the amine complex.
Alternatively, the solid adsorbent, which is utilized to adsorb the metal, may be impregnated with the ammonia or ammonia derivative. However, after adsorbing the metal on the solid adsorbent, the latter is then subjected to destruction by means of an oxidation step followed by additional steps important to recover the metal.
Another patent, namely U.S. Pat. No. 3,948,769, discloses a process for removing ammonia from solutions of waste water. However, this patent does not relate to the art of recovering metal values such as cobalt in a cobalt recovery process, but teaches merely the regeneration of an exchange medium such as a synthetic resin containing an ammonia complex by contacting the medium with low pressure steam, hot water, or hot air.
As will hereinafter be set forth in greater detail, it has now been discovered that metals, and particularly cobalt, may be recovered in greater yields during the hydrometallurgical recovery of other metals, such as nickel, by utilizing solid adsorbents which have been subjected to a pretreatment step prior to their use as adsorbents.